An electric motor drive device for an electric power steering apparatus has been known. For example, JP2015-134598A (corresponding to US2015/0180316A) discloses the electric motor drive device, in which O-rings are respectively installed at an installation location between a connector case and a heat sink and an installation location between the heat sink and a motor cover.
In the electric motor drive device of JP2015-134598A (corresponding to US2015/0180316A), in a case where an electronic control unit is exposed to a temperature change to cause warping of a corresponding constituent member, a compression ratio of the corresponding O-ring may possibly be reduced to cause deterioration of waterproofness of the electric motor drive device.